Home         Authors   Papers   Year of conference   Themes   Organizations        To MES conference

Design of High-Speed Thermocouple Sensors based on SOI Structures
Authors
	Khafizov R.Z.
Date of publication
	2022
DOI
	10.31114/2078-7707-2022-4-193-197
Abstract
	The potential capabilities of modern silicon technology allow to use uncooled thermal sensors for the registration of IR radiation. Among them, we can highlight thermal MEMS sensors, the functioning of which is based on the use of the thermoelectric effect [1,2]. The efficiency of thermal sensors is evaluated using Figure of Merit (FOM) [3], which is the product of the noise–equivalent temperature difference (NETD) and its thermal relaxation time constant τ_r. NETD characterizes the sensitivity of the device, and τ_r is the reaction time to a change in thermal relief in the focal plane of the photodetector and the degree of blurring of the image of moving objects. The smaller the FOM, the better the sensor. However, the thermal mechanism of IR radiation conversion does not allow both NETD and τ_r to be effectively reduced at the same time. Therefore, when designing focal plane arrays (FPA) with thermal sensors, it is necessary to take into account their intended purpose. High sensitivity is necessary to solve the problems of highly sensitive detection of low-contrast targets at a longer range, while low values of τ_r are essential for applications where recording of rapidly changing events is required. Therefore, today a number of works are devoted to solving the problems of reducing τ_rto increase the performance FPAs with thermal detectors [4]. The values of τ_r required for specific applications are provided by the choice of structural, thermophysical and photovoltaic parameters of sensor structures and are implemented in the process of testing the technology of their manufacture [5-6]. In this paper, on the basis of thermophysical analysis, the main design parameters of MEMS thermocouple sensors with a SOI structure are determined, providing the possibility of implementing a thermal relaxation time constant up to 1.5-2 ms in order to increase the frame frequency of IR FPA based on them to 150-200 Hz. The SOI structure, as the basis for the thermopile sensor, makes it possible to use a Si-device layer as a sacrificial layer. Insulating vertical deep trench isolation and buried 〖SiO〗_2 layer (BOX) of the SOI structure, having a high selectivity of etching with respect to silicon, make it possible to effectively form a cavity under the membrane and consoles. In this case, the membrane and consoles can be formed from silicon dioxide, which has a low thermal conductivity. Theoretical evaluation and analytical modeling of thermophysical parameters of thermocouple sensors were carried out, taking into account the requirements for sensor sizes, their sensitivity and the thermal relaxation time constant. The main ratios of the structural elements of the sensitive cells are determined, taking into account the characteristics of the technological layers included in the membrane structure. The obtained results are used as initial data for the topological design of sensor elements and matrix arrays based on them. The topology of crystals with thermocouple sensors was designed taking into account the capabilities of technological equipment (design rules 0.8 microns).
Keywords
	micro-electro-mechanical system (MEMS), thermoelectric effect, IR thermopile sensor, figure of merit (FOM), noise–equivalent temperature difference (NETD), SOI structure, thermal relaxation time constant
Library reference
	Khafizov R.Z. Design of High-Speed Thermocouple Sensors based on SOI Structures // Problems of Perspective Micro- and Nanoelectronic Systems Development - 2022. Issue 4. P. 193-197. doi:10.31114/2078-7707-2022-4-193-197
URL of paper
	http://www.mes-conference.ru/data/year2022/pdf/D073.pdf